Move ReferencedSurfaceTracker into GpuCompositorFrameSink.

services/ui/ws/test_server_window_delegate.cc

Index: services/ui/ws/test_server_window_delegate.cc
diff --git a/services/ui/ws/test_server_window_delegate.cc b/services/ui/ws/test_server_window_delegate.cc
index 6465ac48d7974682b9043282a3527c00ff9aecc7..32cd20306e37cc1e20cb9fe3c016de71f7d947fa 100644
--- a/services/ui/ws/test_server_window_delegate.cc
+++ b/services/ui/ws/test_server_window_delegate.cc
@@ -17,10 +17,6 @@ cc::mojom::DisplayCompositor* TestServerWindowDelegate::GetDisplayCompositor() {
   return nullptr;
 }
 
-const cc::SurfaceId& TestServerWindowDelegate::GetRootSurfaceId() const {
-  return root_surface_id_;
-}
-
 ServerWindow* TestServerWindowDelegate::GetRootWindow(
     const ServerWindow* window) {
   return root_window_;